Because you never know what trivial bit of information may ultimately prove to be vitally important.
Some I remember from the sixties:"Excuse me while I kiss this guy" Purple Haze by Jimi Hendrix"Secret Asian man" Secret Agent Man by Johnny Rivers"Reverend Blue Jeans" Forever in Blue Jeans by Neil Diamond
I had heard of "kiss this guy" because several years ago I came across a web archive of misheard lyrics called kissthisguy.com.But Reverend Blue Jeans...that's a good one. Made me laugh right out loud.
When my younger brother was around four years old and singing Christmas carols, I remember him singing "Hark the hairy angels sing", which brought up all sorts of mental images.